Rolling mill for rolling or sizing metallic pipes, bars or wires

ABSTRACT

A rolling mill for rolling or sizing of metallic pipes, bars and wires has a plurality of rolling units which are arranged on a straight line close to one another and can be exchanged jointly, only a few, or individually, each of the rolling units having at least three rollers which are arranged in a star-like configuration around a rolling axis, drive shafts and motors each driving a respective one of the rollers in all the rolling units, a rolling unit housing provided for the rolling units, roller bearings provided for the rollings, and multi-part rolling shafts provided for supporting the rollers so that the rollers can be exchanged without dismounting of the rolling unit housing and the roller bearings.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a rolling mill for rolling or sizing of metallic pipes, bars, or wires.

[0002] Patent document WO 98/06515 discloses a rolling mill which includes a plurality of rolling units arranged on a straight line close to one another. The rolling units are arranged exchangeably in the rolling mill. They each have three rollers which are arranged in a star-shaped configuration around a rolling axis. Only some rolling units, namely two last rolling units arranged at the outlet side, have rollers which are each driven from an own drive shaft. The remaining rolling units, which are provided in a substantially greater number, have each only one drive shaft which drives directly the roller shaft of each roller which has a horizontally extending rotary axis. The torque of the drive shaft is transmitted to the both other roller shafts by means of bevel gears which are arranged on all roller shafts. In order to retain the bevel gears in engagement with one another, in these rolling units a significant radial adjustment of the roller shafts and thereby of the rollers is not provided. For the both last rolling units arranged at the outlet side, the rollers can be however adjusted in a radial direction since they are driven individually and are supported radially movably.

[0003] This known rolling mill has a substantial disadvantage that the majority of the rolling units, namely those with only one drive shaft, can not be loaded sufficiently high. The reason for this is that, the roller bearings for receiving the forces and the bevel gears for transmission of the torque must be arranged within a equilateral triangle which is formed by the rotary axes of the rollers. Thereby the outer dimensions of the roller bearings and of the bevel gears are limited and as a result the magnitude of the rolling forces to be received and the torque to be transmitted are limited as well. An increase of the triangle of the rotary axis would lead to greater rollers. Greater rollers however increase the distance between the roller units, which leads to an increase of the fraction of unusable, not measurable end portions of the rolling pbaruct. Moreover, greater rollers are more expensive for the manufacture and treatment. Further, with greater rollers, higher investment cost are needed for the whole rolling mill. Therefore an increase of the triangle of the rotary axes can not be considered as an acceptable solution of the problem.

[0004] In addition to their insufficient loading ability, the rolling units with only one driving shaft has the disadvantage, that with such rolling units the arrangement inside the rolling unit housing is especially expensive, since in addition to the roller bearings also the bevel gears must be accommodated inside the triangle of the rotary axes. A radial adjustment of the rollers is possible, but only with substantial structural expenses. High structural expenses without the neller adjustment lead to many components and thereby to high manufacturing and operational costs.

[0005] The expensive arrangement inside the rolling unit housing has a further disadvantage in that, the exchange of the rollers is complicated and time consuming. For this purpose it is necessary to open the rolling unit housing and to partially dismount the roller bearings as well as the bevel gears. After the roller exchange, a corresponding mounting expense is needed. For saving mounting work and time, the rollers in the built-in condition are post-treated. However, for this purpose additional special machines are required.

[0006] In the known rolling mill a substantially great part of the rolling units has each only one drive shaft and thereby the rolling mill has all disadvantages of these rolling units. The rolling mill is not sufficiently loadable, it has complicated and therefore expensive rolling units and requires a high expense for exchange and post-treatment of the rollers.

[0007] In order not to put up with more disadvantages, in the known rolling mill the radial adjustability of the rollers in the rolling units with only one drive shaft and thereby in the majority of the roller units is dispensed with. This leads in such rolling units to substantially increased costs, since in such units the rolling units are used up faster. In rolling units without or without sufficient radial adjustability, worn up rollers must be post-treated with a great material removal. Also unfavorable rolling programs require with these rolling units extensive material removals.

SUMMARY OF THE INVENTION

[0008] Accordingly, it is an object of the present invention to provide a rolling mill for rolling or sizing metal pipes, or and wires, which does not possess the above mentioned disadvantages, but instead can be loaded higher, and also can be adjusted faster as well as with lower expense of labor, time and costs to changing requirements of the operation.

[0009] In keeping with these objects, the above mentioned problem is resolved in an inventive rolling mill for rolling or sizing of metal pipes, bars, or wires, which has a plurality of rolling units arranged on a straight line close to one another and which can be exchanged fast jointly, a few, or individually, and each having at least three rollings arranged in a star-shaped configurations around a rolling mill axis, wherein in all rolling units all rollers and drive shafts are driven from its own motor, and the rollings are supported by multi-part rolling shafts and can be exchanged without dismounting of a rolling unit housing and rolling bearings. This objective is achieved by the combination of the above mentioned features.

[0010] Thereby a rolling mill is provided which, with the same dimensions of its rollers and rolling units, is loadable considerably higher, since all rollings of all rolling units of the rolling mill have an own drive shaft driven directly from its own motor, and therefore the bevel gears for transmission of the torques of the individual rolling shafts are dispensed with. Therefore, inside the equi-lateral triangle which is formed by the rotary axes of the rollings, a free space is formed which otherwise would be required for the bevel gears. This free space can be used completely or partially for the rolling bearings, so that they can be designed greater and therefore with higher supporting ability without increasing the triangle which is formed by the rotary axes of the rollings and thereby without increasing the rollings. The greater rolling bearings makes possible also higher rolling forces with the rollings of the same size and the remaining small distance of the rolling units. Moreover, the torques which act on the rollers are independent of the transmission ability of the bevel gears and can be greater. Finally, it is possible to roll rolling pbaructs with a higher strength or with a lower rolling temperature. Also, the rolling units can be pbaruced with lower expenses and mounted simpler, while the bevel gears and other individual parts can be dispensed with.

[0011] The multi-part design of the rolling shaft makes possible an axial clamping of the rollers each between the facing end surfaces of the two partial shafts. Thereby strength-reducing connections between the rollings and the rolling shafts with keys or similar elements, which are often utilized, are avoided. The multi-part design of the rolling shafts first of all makes possible a fast rolling exchange. For this purpose the axial clamping force between the both part shafts is released, they are moved a little from one another, and the rollers can be removed in a radial direction from the rolling unit. After this, another rolling can be inserted in a radial direction into the rolling unit between the both part shafts and clamped there. A dismounting of the rolling unit housing and/or the rolling bearing is not performed. Such a fast rolling exchange provides for a possibility for using less rolling units, since the preparation time for a new use for the rolling units which are not located in the rolling mill is so short, that they are already available when the rolling units in use must be exchanged. Therefore in the new rolling mill hardly no more than two sets of rolling units are needed. Moreover, with the fast and simple rolling exchange, also a post-treatment of the rollings in the built-in condition and the special machine which are needed for this are superfluous, since the rollings can be dismounted and mounted fast for post-treatment on unitard power tools. Since moreover all rolling units of the rolling mill can be exchanged fast jointly or only a few, or individually, the rolling mill has less and shorter stoppages.

[0012] In accordance with a preferable embodiment of the invention, the rolling units have a one-part rolling unit housing. It is possible because of the inventive individual drive of the rollers and the elimination of the bevel gears. As a result, the rolling unit housing can be produced with significantly lower expenses, since the partial surfaces which are treated with great care and in several steps and then are sealed are also dispensed with, and also numerous openings for keys and connecting screws which otherwise must connect the both parts of the rolling unit housing in alignment with one another.

[0013] In the inventive rolling mill the rollers of all rolling units, of only for a few or of no rolling units can be adjustable. Which possibility is selected depends on the rolling program and the respective operation conditions, for which the rolling mill must be suitable. It is especially however advantageous when in all rolling units the rolling bearings are arranged in eccentric bushings and they can be turned in a stepwise manner for radial adjustment of the rollers and also arrested in several rotary positions. In this manner in all rolling units several distances between the rolling mill axis and the rotary axes of the rollers are available. Rollers with wear down working surfaces can be treated in such a rolling mill to the same calibrating shape and size as the original ones, and then used again. Also, the smaller ideal rolling diameter produce positively during post-treatment and thereby other distances between the rolling mill axis and the rolling rotary axes can be adjusted by turning of the eccentric bushings. The rollers not only can be utilized again, but also at the same unit position and with the same calibrating opening. The relatively expensive rollers can be used so much more frequently that the rolling costs are reduced significantly. The radial adjustment of the rollers can be carried out with a low expense, since in the inventive rolling mill no out bevel gears are provided. It can be performed preferably outside of the rolling line, for example in a work station.

[0014] It is further recommended that at least in the two last rolling units arranged at the outlet side, the roller bearings are arranged in eccentric bushings, and they are formed radially adjustably in a stepless manner for a stepless radial adjustment of the rollers also when the rolling units are assembled ready for operation. They are adjustable regardless whether in the remaining rolling units the rollers are steplessly adjustable or not. This has the advantage that in the finishing region of the rolling mill, all thinkable manufacturing dimensions of the rolling pbaruct can be obtained and also in any sequence. To a limited extent a change of the final dimensions is possible without a change of rollers or rolling units. With this embodiment is also possible to provide a stepped, radial adjustment outside of the rolling mill for all or a few rolling units whose rollers are not steplessly radially adjustable when the rolling units are assembled ready for operation.

[0015] As a rule, the number of the rolling units whose rollings with the rolling unit ready for operation are not steplessly radially adjustable, is greater than the number of the rolling units with steplessly radially adjustable rollings. Thereby the expenses and the cost for the pbaruction of the rolling mill are reduced, since a minimum of expensive rolling units with steplessly radially adjustable rollings are utilized.

[0016] It is also advantageous when the rolling units whose rollers are not steplessly radially adjustable with the rolling unit assembled ready for operation, have rollers with a different ideal rolling diameter than the rolling units with the steplessly radially adjustable rollers. This improves the possibilities of a new use for post-treated rollers and also saves roller costs.

[0017] It is also desirable that all unit positions are suitable for rolling units with steplessly radially adjustable rollers and for rolling units with not steplessly radially adjustable rollers. It is thereby possible to use all rolling units on all unit positions and to adapt the rolling mill better to the corresponding requirements.

[0018] In accordance with a recommended embodiment the drive shafts of the rollers and the shafts of their motors extend coaxially to the corresponding rolling rotary axes. It is especially advantageous when the motors with the shafts which form an angle to a horizontal plane and assume the same angular position to one another are arranged on or in a joint frame. This simplifies the devices for coupling the rolling units to and uncoupling the rolling units from the drive of their rollers during exchange of the rolling units. Also, the exchange of the rolling units is thereby accelerated and the actual stoppages of the rolling mill are shortened. Preferably, a reducing transmission is arranged on or in a joint frame between the motors and the drive shafts of the rollers. It is considered to be advantageous when the reducing transmission is formed as a planetary transmission.

[0019] In accordance with a further embodiment of the present invention the reducing transmissions of several or all motors with the same angular position are assembled in a housing which is formed as a joint frame. Here also several or all motors with the same angular position can be flanged on a housing of the reducing transmission, formed as a joint frame. In accordance with another embodiment, the motors and reducing transmissions of one or several rollers whose rolling rotary axes form an angle with a horizontal plane, are assembled to form a drive unit.

[0020] It is especially advantageous when the joint frame or frames or drive units are linearly displacable in direction of the associated rotary axis of the rollers. It is however also possible that the joint frame or frames or drive units are turnable about a turning axis extending parallel to the rolling mill axis. Therefore for turning of the joint frames or drive units a hinge transmission can be provided. It is also advantageous when the joint frame or frames or drive units arranged above the rolling mill axis are supported by a supporting bridge of concrete. Such a supporting bridge provides all possibilities for mounting of the frames or drive units and acts in a damping manner for eventually occurring vibrations.

[0021] An unit exchanging device is provided for removing the rolling units simply and fast as well as jointly or only a few or individually from the rolling line of the rolling mill, and exchanging by other rolling units. In a recommended embodiment one or several rolling units are arranged on one or several unit changing cars from which they can be moved into the rolling line or onto which they can be moved from the rolling line. The unit changing cars perform the displacement of the rolling units in or opposite to the rolling direction along the rolling mill. They can be also used for transportation of the rolling units from the rolling mill to a unit workshop and back.

[0022] In this embodiment of the rolling mill, the drive for moving the rolling unit can be arranged under the motors and in some cases the reducing transmission for the rollings with horizontally extending rotary axes. The drive can have a number of horizontally extending working cylinders which can be coupled selectively to an associated rolling unit on a unit changing car or in a unit receptacle of the rolling mill. As an alternative, the drive for moving the rolling units can have two horizontally extending work cylinders. They can be arranged in the region of the end faces of the rolling mill which are located at the inlet and at the outlet. They engage a transporting beam which is arranged on the operational location of the rolling units, extends parallel to the rolling mill axis and is displaceably transversely to the latter. Each rolling unit can be selectively coupled to the transporting beam.

[0023] In accordance with another embodiment of the rolling mill, one or several rolling units unit on one or several unit changing cars, and the rolling units with the unit changing cars are movable in and out of the rolling line. Then the unit changing cars are used for holding the rolling units during the rolling.

[0024] The novel features which are considered as characteristic for the present invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0025]FIG. 1 is a plan view of a rolling mill in accordance with the present invention;

[0026]FIG. 2 is a view showing a section taken along the line II-II in FIG. 1;

[0027]FIG. 3 is a view showing a rolling mill corresponding to FIG. 2, but provided with a turnable upper rolling drive;

[0028]FIG. 4 is a side view of a rolling mill corresponding to FIG. 3, but provided with another rolling exchanging device; and

[0029]FIG. 5 is a view showing a rolling mill corresponding to FIG. 3, but provided with a hinge transmission for turning of the upper rolling drive.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0030]FIG. 1 shows a rolling mill 1 with a great number of rolling units 2. Several rolling units are arranged on a unit changing car 3 closely to one another. The rolling units 2 on the unit changing car 3 come out of a unit workshop, where the rolling units 2 are prepared to be introduced into the rolling mill 1 and where they can be placed in the required sequence on the unit changing car 3. Tracks 4 lead to the rolling mill 1. A second unit changing car 5 with empty unit receptacles 6 is located before it, while its rolling units 2 are located in the rolling mill 1 and therefore can not be seen on the plan view of FIG. 1. These rolling units 2 when needed can be moved from the rolling mill 1 onto the units changing car 5 all together, only a few or individually. They move to the side, so that the unit changing car 3 can move with its other rolling units 2 in front of the rolling mill 1. Then the rolling units 2 on the unit changing car 3, which are required in the rolling mill 1 are brought to their unit positions in the rolling mill 1.

[0031] In FIG. 2 the unit changing car 5 is shown in a cross-section. Dash-dot lines identify the position of the rolling unit on the unit exchanging car 5, after it was removed from the rolling mill 1. The rolling unit 2 actually is located in FIG. 2 in its operational position. Three rollers 7 are arranged in a star-liked configuration in the rolling unit 2. They surround a straight horizontal rolling mill axis 8 which is illustrated in FIG. 2 only as an intersection point.

[0032] All rollers 7 are driven separately. Each drive is performed through a drive shaft 9 from a motor 10. Lowering transmissions 11 are arranged between the drive shafts 9 and the motors 10. They are formed as planetary transmissions. The drive shafts 9, motors 10 and lowering transmissions 11 which are not provided with reference numerals are associated with a neighboring rolling unit 2.

[0033] At each unit position, a work cylinder 12 which can extend horizontally is located under the motors 10, the lowering transmissions 11 and the drive shafts 9 for the rollings 7 with horizontally extending rotary axes. It can be selectively coupled with the associated rolling unit 2, so that it can be displaced from the rolling mill 1 out on a unit changing car 3, 5 or pulled from the unit changing car 3, 5 into the rolling mill 1.

[0034] The motors 10 and the lowering transmissions 11 whose shafts form an angle to a horizontal plane and which assume the same angular positions relative to one another are arranged on a common frame 13. The frames 13 can be linearly displaced by a further work cylinder 14 in direction of the facing rotary axes of the rollings 7. Couplings 15 provide a possibility for separating and coupling of the drive shafts 9 with the rolling shafts 16, which are located hardly completely in the rolling units 2 and therefore can not be seen in FIG. 2. When pressurized medium is correspondingly supplied to the work cylinder 14, the joint frames 13 and with them the motors 10, the lowering transmissions 11 and the drive shafts 9 are moved from the rolling units 2 so that, the parts of the couplings 15 are separated and the rolling units 2 can be displaced horizontally, for example onto the unit exchanging car 5. The couplings 15 of the horizontal extending drive shafts 9 also release. Correspondingly the rolling shafts 16 of the rolling units 2 can be again coupled with the drive shafts 9, when the rolling units 2 are located in their operational position. The frames 13 are then moved by the work cylinders 14 to the rolling units 2 until the parts of the couplings 15 are again engaged with one another.

[0035] The joint frame 13 arranged in FIG. 2 above the rolling mill axis 8 is held by a supporting bridge 17 of concrete. In the embodiment shown in FIG. 3 this is not the case. There the joint frame 13 arranged above the rolling mill axis 8 is held by at least one turning arm 18 which is turnable about a turning axis 19 extending parallel to the rolling mill axis 8. The turning movement can be performed both of work cylinders and also of motors, which however is not shown in FIG. 3. The turning movement of the upper frame 13 releases not only the couplings 15, but also it can be performed so far that the region above the rolling unit 2 is free and the rolling unit 2 can be engaged from above with a crane and therefore exchanged. There is also a possibility to operate without the unit changing cars 3, 5. In other aspects the embodiment of FIG. 3 corresponds to that of FIG. 2.

[0036]FIG. 4 shows a rolling mill of FIG. 3 but with another device for fast exchange of the rolling units 2. A transporting beam 20 is arranged at the operation side of the rolling unit 2. It extends parallel to the rolling mill axis 8 and is displaceable transversely to it. The transporting beam 20 is driven by two work cylinders 21 which are supplied with pressurized medium. Each of the work cylinders is arranged in the region of end faces of the rolling mill 1 at the inlet side and outlet side, so that in FIG. 2 only one of the work cylinders can be seen. Each rolling unit 2 can be coupled with the transporting beam 20 by a catch 22 arranged on each unit position and turnable about a hinge 23. For this purpose the catch 22 which is turnable by hand engages in a recess 24 of the associated rolling unit 2.

[0037] During exchange of the rolling units 2, the transporting beam 20 together with the coupled rolling units 2 is displaced onto the unit changing car 5. Then the transporting beam 20 is uncoupled from its work cylinders 21, and they are moved back to their initial position. The unit changing car 5 can then move together with the transporting beam 20 to a unit workshop. The other unit changing car 3 with prepared rolling units 2 also moves a transporting beam 20 on which the work cylinders 21 are coupled, when the unit change car 3 is located in a correct position in front of the rolling mill 1. The prepared rolling units 2 can be moved into the rolling mill 1 by the transporting beam 20.

[0038] The embodiment of the rolling mill of FIG. 5 differs from that of FIG. 3 only by a hinge transmission 25 for holding and moving the upper frame 13, instead of the turning arm or arms 18.

[0039] It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of constructions differing from the types described above.

[0040] While the invention has been illustrated and described as embodied in rolling mill for rolling or sizing metallic pipes, bars or wires, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.

[0041] Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications without omitting features that, from the unitpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention. 

What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims:
 1. A rolling mill for rolling or sizing of metallic pipes, bars and wires, comprising a plurality of rolling units which are arranged on a straight line close to one another and can be exchanged jointly, only a few or individually, each of the rolling units having at least three rollers which are arranged in a star-like configuration around a rolling mill axis; drive shafts and motors each driving a respective one of said roller in all said rolling units; a rolling unit housing provided for said rolling units; roller bearings provided for said rollers; and multi-part rolling shafts provided for supporting said rollers so that said rollers can be exchanged without dismounting of said rolling unit housing and said rolling bearings.
 2. A rolling mill as defined in claim 1, wherein said roller unit housing of said roller units is a one-part roller unit housing.
 3. A rolling mill as defined in claim 1; and further comprising eccentric bushings in which said rolling bearings of all said roller units are arranged, said eccentric bushings being turnable in a stepped fashion and arrestable in several rotary positions for radial adjustments of said rollings.
 4. A rolling mill as defined in claim 1, wherein at least two of said rolling units located at an outlet side of the rolling mill have eccentric bushings in which said rolling bearings are arranged, said rolling bearings of said at least two rolling units being steplessly radially adjustable when said rolling units are built-in and ready for operation, for stepless radial adjustment of said rollers.
 5. A rolling mill as defined in claim 4, wherein said rolling units include such rolling units, whose rollers with the rolling units which are built-in and ready for operation are not steplessly radially adjustable, are radially adjustable in a stepped-fashion outside the rolling mill.
 6. A rolling mill as defined in claim 5, wherein a number of said rolling units, whose rollers with the rolling units built-in and ready for operation are not steplessly radially adjustable, is greater than a number of the rolling units with the rollers which are steplessly radially adjustable.
 7. A rolling mill as defined in claim 4, wherein said rolling units, whose rollers with the built-in and ready for operation rolling units are not steplessly radially adjustable, have rollers with a different ideal rolling diameter than said rolling units with steplessly radially adjustable rollers.
 8. A rolling mill as defined in claim 5, wherein all unit positions are suitable for said rolling units with steplessly radially adjustable rollers and for said roller units with not steplessly radially adjustable rollers.
 9. A rolling mill as defined in claim 1, wherein said drive shaft of said rollers and said shafts of said motors extend coaxially to a corresponding rolling rotary axis.
 10. A rolling mill as defined in claim 1; and further comprising a joint frame said motors with shafts forming an angle to a horizontal plane and having the same angular position relative to one another, being arranged on, at or in said joint frame.
 11. A rolling mill as defined in claim 10; and further comprising lowering transmissions arranged on said joint frame between said motors and said drive shafts of said rollers.
 12. A rolling mill as defined in claim 11, wherein said lowering transmission is formed as a planetary transmission.
 13. A rolling mill as defined in claim 11; and further comprising a housing in which said lowering transmissions of several or all said motors with a same angular position are accommodated, said housing being formed as a joint frame.
 14. A rolling mill as defined in claim 13, wherein said several or all motors with the same angular position are flanged on said housing of said lowering transmissions, which is formed with said joint frame.
 15. A rolling mill as defined in claim 11, wherein said motors and said lowering transmissions of one or several rollers with rolling rotary axes forming an angle of a horizontal plane are assembled to one drive unit.
 16. A rolling mill as defined in claim 15, wherein one or several joint frames or drive units are linearly displaceable in direction of associated rolling rotary axes.
 17. A rolling mill as defined in claim 16, wherein one or several said joint frames of said drive units are turnable about a turning axis extending parallel to said rolling mill axis.
 18. A rolling mill as defined in claim 17; and further comprising a pivot transmission provided for turning of said joint frames or said drive unit.
 19. A rolling mill as defined in claim 15; and further comprising a supporting bridge composed of concrete and supporting one or several joint frames or drive units above the rolling mill axis.
 20. A rolling mill as defined in claim 1; and further comprising one or several unit changing cars on which one or several rolling units are located, so that said rolling units can be moved from unit changing cars into a rolling line or moved onto said unit changing cars from said rolling line.
 21. A rolling mill as defined in claim 20; and further comprising a drive for moving said rolling units, said drive for moving said rolling units being arranged under said motors of the rollers, and optimally a lowering transmission which have horizontally extending rotary axes, said drive having a plurality of horizontally extending work cylinders which are selectively couplable to an associated one of several rolling units on one of said unit changing cars or in a unit receptacle of the rolling mill.
 22. A rolling mill as defined in claim 20; and further comprising a drive for moving said rolling units and including two horizontally extending work cylinders which are arranged in a region of inlet-side and outlet-side end faces of the rolling mill and a transporting beam at an operation side of said rolling units, said transportation beam extending parallel to said rolling mill axis; and is engaged by said working cylinders extending transversely to said rolling mill axis, the transporting beam being formed so that each of said rolling units can be selectively coupled with it.
 23. A rolling mill as defined in claim 1; and further comprising one or more unit changing cars on which one or more rolling units are arranged, so as to move said rolling units into said rolling line or from said rolling line. 